[PATCH v2 02/13] tap: Clean up behaviour for errors on listening Unix socket

[David Gibson <david@gibson.dropbear.id.au>]

We call tap_sock_unix_new() to handle a new connection to the qemu socket
if we get an EPOLLIN event on c->fd_tap_listen.  If we get any other event
on the fd, we'll fall through to the "tap reset" path.  But that won't do
anything relevant to the listening socket, it will just close the already
connected socket.  Furthermore, the only other event we're subscribed to
for the listening socket is EPOLLRDHUP, which doesn't apply to a non
connected socket.

Change the subscribed events from EPOLLRDHUP to EPOLLERR to catch general
errors - not that there's any obvious case that would cause this event on
a listening socket.  Since we don't really expect it, and it's not obvious
how we'd recover, treat it as a fatal error if we ever do get that event.

Finally, fold all this handling into the tap_sock_unix_new() function,
there's no real reason to split it between there and tap_handler().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tap.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tap.c b/tap.c
index b4967d0..c883d7e 100644
--- a/tap.c
+++ b/tap.c
@@ -1108,7 +1108,7 @@ static void tap_sock_unix_init(struct ctx *c)
 	listen(fd, 0);
 
 	ev.data.fd = c->fd_tap_listen = fd;
-	ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
+	ev.events = EPOLLIN | EPOLLERR | EPOLLET;
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap_listen, &ev);
 
 	info("You can now start qemu (>= 7.2, with commit 13c6be96618c):");
@@ -1121,14 +1121,18 @@ static void tap_sock_unix_init(struct ctx *c)
 /**
  * tap_sock_unix_new() - Handle new connection on listening socket
  * @c:		Execution context
+ * @events:	epoll events
  */
-static void tap_sock_unix_new(struct ctx *c)
+static void tap_sock_unix_new(struct ctx *c, uint32_t events)
 {
 	struct epoll_event ev = { 0 };
 	int v = INT_MAX / 2;
 	struct ucred ucred;
 	socklen_t len;
 
+	if (events != EPOLLIN)
+		die("Error on listening Unix socket, exiting");
+
 	len = sizeof(ucred);
 
 	/* Another client is already connected: accept and close right away. */
@@ -1284,8 +1288,8 @@ static void tap_sock_reset(struct ctx *c)
 void tap_handler(struct ctx *c, int fd, uint32_t events,
 		 const struct timespec *now)
 {
-	if (fd == c->fd_tap_listen && events == EPOLLIN) {
-		tap_sock_unix_new(c);
+	if (fd == c->fd_tap_listen) {
+		tap_sock_unix_new(c, events);
 		return;
 	}
 
-- 
@@ -1108,7 +1108,7 @@ static void tap_sock_unix_init(struct ctx *c)
 	listen(fd, 0);
 
 	ev.data.fd = c->fd_tap_listen = fd;
-	ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP;
+	ev.events = EPOLLIN | EPOLLERR | EPOLLET;
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, c->fd_tap_listen, &ev);
 
 	info("You can now start qemu (>= 7.2, with commit 13c6be96618c):");
@@ -1121,14 +1121,18 @@ static void tap_sock_unix_init(struct ctx *c)
 /**
  * tap_sock_unix_new() - Handle new connection on listening socket
  * @c:		Execution context
+ * @events:	epoll events
  */
-static void tap_sock_unix_new(struct ctx *c)
+static void tap_sock_unix_new(struct ctx *c, uint32_t events)
 {
 	struct epoll_event ev = { 0 };
 	int v = INT_MAX / 2;
 	struct ucred ucred;
 	socklen_t len;
 
+	if (events != EPOLLIN)
+		die("Error on listening Unix socket, exiting");
+
 	len = sizeof(ucred);
 
 	/* Another client is already connected: accept and close right away. */
@@ -1284,8 +1288,8 @@ static void tap_sock_reset(struct ctx *c)
 void tap_handler(struct ctx *c, int fd, uint32_t events,
 		 const struct timespec *now)
 {
-	if (fd == c->fd_tap_listen && events == EPOLLIN) {
-		tap_sock_unix_new(c);
+	if (fd == c->fd_tap_listen) {
+		tap_sock_unix_new(c, events);
 		return;
 	}
 
-- 
2.41.0